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I've been reading but I guess I am confused. My KH value is low and I am having trouble controlling it. Here are the test readings on my system

SG=1.26 or 35 depending on the scale
CA=450
MG=1400
KH=6.7 Which I know is low
PH=7.9
Nitrates= 0
Nitrites=0
Ammonia=0
PO4=.16ish hard to read exactly but between .16 and .08 I run phosban to keep it down. This is confusing also I see some things that say it can be higher other things say keep it close to zero.

I change about 10% of my water every 2 weeks. I change it daily 8000ML per 24 hours the system is 150 Gal plus about 15Gal in the sump. At this rate the CA and MG stays steady. The new salt water has a KH of 10.7.

I can hand add something to raise the KH but it is not consistent and I'd like to do something to keep it more constant. I have a dosing unit. Is that the simplest way and what would you recommend be dosed?

well..
first.. you need to decide where you want to keep your alk... (I'd recommend 8-8.5)
Then slowly dose it up to that level using just baking soda/water (or the alk component of a 2 part mix or whatever)..
Then determine the consumption rate (daily or whatever) then you can dial in a correct daily dosage amount of the alk component of a 2 part mix..

Then start dosing/testing/adjusting as necessary..

Personally I'd just get a bunch of sodium bicarbonate (baking soda) and mix up a proper mix http://reefkeeping.com/issues/2006-02/rhf/index.php
and start using it manually (straight sodium bicarbonate first so its more concentrated) to raise your level up slowly (no more than like .5-1dkh a day)
And measure/adapt as needed to keep it stable..

There are calculators too to help determine initial dosage amounts based on known consumption rate,etc...